Generally, a locking device or a door latch provided for a door includes a latch bolt unit installed on an inner side surface of the door to move forward (project) or move backward (retract) in accordance with a rotation of a door outer lever type or a round-shaped ball handle. The projecting movement of the latch bolt unit refers to a movement of popping out of the door, while the retracting movement of the latch bolt unit refers to a movement of entering inside the door.
Such latch bolt unit has a front end having a curved portion that is rounded such that automatic door closing is enabled even when the door in a projected state is closed without the lever operation, because the inclined surface is brought into contact with the threshold or a wall and retracted automatically.
A latch bolt unit insertion hole is formed in the doorframe or the wall to receive the latch bolt unit inserted therein and this structure allows the latch bolt unit to be inserted into the latch bolt unit insertion hole upon door closing. Accordingly, as described above, even when the door is closed without lever turning, the latch bolt unit is pushed by the doorframe or wall to be automatically retracted and when moved to a location where the bolt insertion hole is formed in the doorframe or the wall, the latch bolt unit is projected outward by the elastic returning force of an internally-loaded spring to thus maintain the door in the closed state.
Once a locking device is operated with the door being kept in the closed state in the manner described above, it is impossible to open the door from outside by turning the lever. In order to release the lock, manipulation inside the door to unlock, or manipulation with a key outside the door to unlock is necessary.
However, the presence of the inclined surface of the latch bolt unit allows an external intruder to retract the latch bolt unit by force by forcefully inserting a plastic card or other member through a chink of the door from outside, thus forcefully unlocking the locked state. This would cause safety issues.
A door is classified into a left handed door opened in a left-arm direction, and a right handed door opened in a right-arm direction. Because a door latch (i.e., locking device) has an opposite direction of installation according to whether the door is the left handed door or the right handed door, the direction of rotation of the lever is reversed with respect to the door latch. Accordingly, installations and uses of the door latch for one single direction are limited, as the door latch is designed for either the left handed door or the right handed door.
A hole for installation purpose is formed in an entrance door when a door lock is installed on the entrance door, and there are mainly two types of standardized entrance doors that have about 60 mm or about 70 mm of backset (i.e., distance from an edge of the entrance door to the center of the hole for installation).
Accordingly, it is inconvenient because the respective door latches have to be prepared to conform to various backset standards of the doors. An adjustable backset is thus necessary for the door latch to allow universal installation and use thereof, irrespective of the different backset standards of the entrance doors. However, a door latch provided with adjustable backset is not disclosed yet.